FIG. 1 is a block diagram showing the configurations of conventional acoustic signal encoding apparatus 10 and acoustic signal decoding apparatus 20. Here, the case will be described where multichannel signals are assumed to be two-channel signals and acoustic signal encoding apparatus 10 down-mixes the two-channel signals to one channel.
First, acoustic signal encoding apparatus 10 will be explained. In FIG. 1, down-mixing coefficient storage section 11 stores a down-mixing coefficient indicating a down-mixing ratio and outputs the down-mixing coefficient to down-mixing section 12.
Down-mixing section 12 mixes the input two-channel signals (multichannel signals) according to the down-mixing coefficient and thereby outputs the down-mixed signal as a one-channel down-mixed signal to multiplexing section 14.
Level difference calculation section 13 receives the same two-channel signals that have been inputted to down-mixing section 12 as input, calculates a level difference between the inputted two-channel signals and outputs the calculated level difference (level difference information) to multiplexing section 14.
Multiplexing section 14 multiplexes the one-channel down-mixed signal outputted from down-mixing section 12 with the level difference information outputted from level difference calculation section 13, forms a bit stream and outputs the formed bit stream from acoustic signal encoding apparatus 10.
Next, acoustic signal decoding apparatus 20 will be explained. In FIG. 1, demultiplexing section 21 extracts the down-mixed signal and the level difference information from the bit stream outputted from acoustic signal encoding apparatus 10 and outputs the extracted down-mixed signal and level difference information to separation section 22.
Separation section 22 forms two-channel signals from the one-channel down-mixed signal outputted from demultiplexing section 21 using the level difference information likewise outputted from demultiplexing section 21.
Here, separation section 22 is described as separating the signal into two-channel signals only using the level difference information, but it is possible to use correlation information and phase information of the two-channel signals in addition to the level difference information.
In this way, according to above-described acoustic signal encoding apparatus 10 and acoustic signal decoding apparatus 20, a multichannel signal can be encoded with a fewer number of channels (for example, see Non-Patent Document 1).
Non-Patent Document 1: “Text of ISO/IEC 14496-3:2001/FPDAM2 July, 2003 of (Parametric Audio)”